Oil separator and outdoor unit with the oil separator

ABSTRACT

An oil separator including a shell ( 50 ) with a cylindrical section and a taper section which narrows in a downward direction and which is formed as an integral part at the bottom of the cylindrical section, an outlet pipe ( 51 ) which is inserted through the top of the shell so that the central axis of the outlet pipe coincides with the central axis of the shell, a discharge pipe ( 52 ) connected to an opening provided at the bottom of the taper section, and an inlet pipe ( 53 ) connected tangentially to the inner surface of the cylindrical section for introducing a gas liquid two phase flow into the shell, wherein the distance between the shell opening ( 50 a) and the tip ( 51 a) of the outlet pipe inside the shell is at least 5 times the inside diameter of the inlet pipe ( 53 ).

TECHNICAL FIELD

[0001] The present invention relates to an oil separator used primarilyin refrigerating devices and air conditioning devices for separatingoil, which is carried out from the compressor along with a refrigerantgas, from the refrigerant gas and then returning this oil to thecompressor, and also relates to an outdoor apparatus using such an oilseparator.

BACKGROUND ART

[0002]FIG. 14 is an internal structural diagram of a conventional oilseparator disclosed in Japanese Patent Laid-Open Publication No. Hei8-319815.

[0003] In FIG. 14, 101 represents a shell of a substantially cylindricalshape, wherein one of open ends 101 a is of a small diameter, and theother open end 101 b is of a large diameter. A taper section 101 c isformed at the open end 101 a, and a flange section 101 f which extendsout in radial direction is formed at the other open end 101 b.Furthermore at the open end 101 b, an inlet pipe 102 is formed as anintegral part of the shell 101, and an inlet port 102 a is formed in theshell 101 in a tangential direction to the inner cylindrical surface ofthe shell 101.

[0004]103 represents an outlet pipe of a cylindrical shape with a collarsection 104 formed around the middle section of the pipe, and thiscollar section 104 has a flange section 104 f which is stuck onto theflange section 101 f of the shell 101.

[0005] In this type of oil separator, a gas liquid mixture of gas andoil mist flows in from the inlet pipe 102 in a tangential direction tothe inner surface of the shell 101 and circles around inside the shell101, and centrifugal force causes the oil mist to separate and adhere tothe inner surface of the shell 101, and then flow down along the innersurface and discharge from the open end 101 a. Furthermore, the gaswhich remains after the oil mist has separated is discharged from theoutlet pipe 103. Because an internal opening of the outlet pipe 103inside the shell is larger than an external opening, the speed of thegas inside the shell 101 is reduced when being drawn into the outletpipe 103, so that oil mist adhering to the outside wall of the outletpipe 103 is prevented from being carried on the gas current and caughtin the outlet pipe 103.

[0006]FIG. 15 is a partial longitudinal sectional view of a conventionaloil separator disclosed in Japanese Patent Laid-Open Publication No. Hei9-177529.

[0007] In FIG. 15, 201 represents a shell, which is provided with acylindrical section 202 a with an integrated flange section 202 bextending outward at its top end. Furthermore, an inverted cone shapedcylinder 202 c is integrally attached to the bottom edge of thecylindrical section 202 a, and an oil recovery section 202 d isintegrally attached to the bottom opening of the inverted cone shapedcylinder 202 c. In addition, an inlet pipe 203 is attached to an openingnear the top end of the cylindrical section 202 a. A circular lid 204 isfixed to the flange section 202 b of the cylindrical section 202 a. Anoutlet pipe 205 passes through the center of the lid 204. A non-wovenfabric 206 of a predetermined shape is attached to the inside of theoutlet pipe 205.

[0008] In this type of oil separator, gas incorporating oil mist flowsfrom the inlet pipe 203 into the shell 201, and circles around withinthe cylindrical space formed between the cylindrical section 202 a andthe outlet pipe 205 extending into the cylindrical section 202 a. As aresult of the cyclone effect resulting from the circling gas, the oilmist in the gas, particularly with a particle diameter of 5 Mm orgreater, collides with the inner surface of the shell 201 and condenses,and when a particle grows to a sufficiently large diameter on the innersurface, gravity causes the particle to slide down the inner surface andflow into the oil recovery section 202 d.

[0009] Furthermore, the oil mist of a smaller particle diameter, whichhas not separated out through collision with the inner surface of theshell 201, flows into the outlet pipe 205 together with the gas. Due tothe effect of the circling motion inside the cylindrical space K, thegas does not pass straight through the outlet pipe 205, but rather movesupwards in a helical type circling motion. At this point, the velocitydistribution of the gas stream is such that the velocity close to thepipe wall is large, whereas the velocity in the center is extremelysmall. The gas which is circling at high speed in a helical type motionaround the periphery hits the non-woven fabric 206 attached to the pipewall and is adsorbed. Repeated adsorption of these minute particlesleads to an increase in the diameter of the particles adsorbed to thenon-woven fabric 206, and particles which have grown sufficiently largemove down the non-woven fabric 206 under the influence of gravity, dropoff the bottom edge of the outlet pipe 205, and are collected in the oilrecovery section 202 d.

[0010]FIG. 16 is a structural diagram showing a conventional gas liquidseparator disclosed in Japanese Utility Model Laid-Open Publication No.Hei 6-60402, and FIG. 17 is a cross-sectional diagram viewed from above.

[0011] In the diagrams, a gas-liquid separator 301 includes a shell 304formed of a combination of a cylinder 302 and a cone 303. Inlet pipes305 for introducing a two phase flow in a tangential direction areprovided on the side of the cylinder 302 of the shell 304, and this twophase flow is separated into a liquid and a vapor by the centrifugalforce produced by the two phase flow circling around inside the shell304, so that the liquid adheres to the inside wall of the shell 304through self adhesion.

[0012] A wick is also provided on the internal wall of the shell 304 forguiding the separated liquid into the cone 303. This wick is providedwith a plurality of narrow grooves 306 of 0.3 to 0.5 mm formed in ahelical pattern, and the force of the circling flow and the capillaryphenomenon causes the liquid to move smoothly to the cone.

[0013] In addition, in order to prevent diffusion of the two phase flowfrom the cylinder 302 to the cone 303, a diaphragm 307 is providedinside the shell 304 to partition the shell into two portions on thesides of the cylinder 302 and the cone 303. The diaphragm 307 isprovided with small apertures 308 for connecting the cylinder 302 sidewith the cone 303 side to maintain a uniform pressure within the shell304. Furthermore, a gap 309 is provided between the outer perimeter ofthe diaphragm 307 and the inner surface of the shell 304. A wire gauzefolded in a wave like pattern is put as a coarse wick, inside the cone303 side of the shell 304 partitioned by the diaphragm 307, andfunctions as a liquid collector 310 for accumulating liquid. A liquidguide pipe 311 for guiding liquid out of the shell 304 is formed at theapex of the cone 303. Furthermore, an outlet pipe 312 is formed in thecenter of the cylinder 302 side of the shell 304 partitioned by thediaphragm 307, so as to pass through the end plate 302 a of the cylinder302 side.

[0014] In this type of conventional oil separator and gas liquidseparator, the ideal positional relationship between the outlet pipe andthe inlet pipes is unclear. Therefore, in systems in which the flow rateof the refrigerant varies in accordance with high pressure and lowpressure fluctuations in the refrigerating cycle caused during loadfluctuations, or in systems in which the compressor controls thecapacity in accordance with the load, the system is unable to dealappropriately with such a problem that though the system operatesappropriately at the time when the refrigerant flow rate is large, thevelocity of the circling gas inside the oil separator falls and the oilseparation efficiency resulting from the cyclone effect declines at thetime when the refrigerant flow rate falls. Here, the oil separationefficiency is the ratio of the volume of oil discharged from thedischarge pipe per a unit of time, relative to the volume of oil flowinginto the oil separator per the unit of time.

[0015] If such a configuration is adopted that the diameter of the inletpipe is reduced at the time of low flow rate in order to alleviate thisproblem, the pressure loss will increase at the time when the gasvelocity flowing into the shell is increased, so that the efficiency ofthe refrigerating cycle will decline.

[0016] Furthermore, in the case where the separated oil cannot besuitably discharged from the oil separator, the volume of oilaccumulated inside the shell increases, and the accumulated oil insidethe oil separator is lifted up by the gas flow inside the oil separatorand flows out of the outlet pipe, producing a problem of a reduction inthe oil separation efficiency.

[0017] In addition, if a diaphragm is provided as shown in FIG. 16, oran adsorbent material such as a non-woven fabric for trapping oil mistis provided in the outlet pipe as shown in FIG. 15, in order to preventthe lifting of oil within the shell, the problem of increased costassociated with the increase in the number of components arises.

DISCLOSURE OF THE INVENTION

[0018] The present invention aims to solve the problems described above,and an object thereof is to provide an oil separator in whichfluctuations in the pressure loss and the oil separation efficiency aresmall even in cases where the velocity of the gas flowing into the oilseparator varies or the amount of oil accumulated inside the shellvaries due to a variation in the flow rate of oil into the oilseparator, and moreover in which the product cost is low.

[0019] An oil separator according to the present invention is an oilseparator comprising a shell having a cylindrical section and a tapersection which narrows in a downward direction and which is formed as anintegral part at the bottom of the aforementioned cylindrical section,an outlet pipe which is inserted through the top of the aforementionedshell so that the central axis of the outlet pipe coincides with thecentral axis of the shell, a discharge pipe connected to an openingprovided at the bottom of the aforementioned taper section, and an inletpipe connected tangentially to the inner surface of the aforementionedcylindrical section for introducing a gas liquid two phase flow into theaforementioned shell, characterized in that the distance between theaforementioned opening and the tip of the outlet pipe inside the shellis at least 5 times the inside diameter of the aforementioned inletpipe.

[0020] Furthermore, an oil separator according to the present inventionis an oil separator comprising a shell having a cylindrical section anda taper section which narrows in a downward direction and which isformed as an integral part at the bottom of the aforementionedcylindrical section, an outlet pipe which is inserted through the top ofthe aforementioned shell so that the central axis of the outlet pipecoincides with the central axis of the shell, a discharge pipe connectedto an opening provided at the bottom of the aforementioned tapersection, and an inlet pipe connected tangentially to the inner surfaceof the aforementioned cylindrical section for introducing a gas liquidtwo phase flow into the aforementioned shell, characterized in that thetip of the outlet pipe inside the shell is positioned below the centerof the inside diameter of the inlet pipe at a distance at least 5 timesthe inside diameter of the inlet pipe.

[0021] Furthermore, an oil separator according to the present inventionis an oil separator comprising a shell having a cylindrical section anda taper section which narrows in a downward direction and which isformed as an integral part at the bottom of the aforementionedcylindrical section, an outlet pipe which is inserted through the top ofthe aforementioned shell so that the central axis of the outlet pipecoincides with the central axis of the shell, a discharge pipe connectedto an opening provided at the bottom of the aforementioned tapersection, and an inlet pipe connected tangentially to the inner surfaceof the aforementioned cylindrical section for introducing a gas liquidtwo phase flow into the aforementioned shell, characterized in that theaforementioned inlet pipe has a straight pipe section connected to theaforementioned cylindrical section, and the length of this straight pipesection is at least 8 times the inside diameter of the inlet pipe.

[0022] Furthermore, an oil separator according to the present inventionis an oil separator comprising a shell having a cylindrical section anda taper section which narrows in a downward direction and which isformed as an integral part at the bottom of the aforementionedcylindrical section, an outlet pipe which is inserted through the top ofthe aforementioned shell so that the central axis of the outlet pipecoincides with the central axis of the shell, a discharge pipe connectedto an opening provided at the bottom of the aforementioned tapersection, and an inlet pipe connected tangentially to the inner surfaceof the aforementioned cylindrical section for introducing a gas liquidtwo phase flow into the aforementioned shell, characterized in that theaforementioned inlet pipe is a bent pipe having a first straight pipesection connected to the aforementioned cylindrical section and a secondstraight pipe section positioned at a 90 degree angle to the firststraight pipe section in the direction of the aforementioned shell.

[0023] Furthermore, an oil separator according to the present inventionis an oil separator comprising a shell having a cylindrical section anda taper section which narrows in a downward direction and which isformed as an integral part at the bottom of the aforementionedcylindrical section, an outlet pipe which is inserted through the top ofthe aforementioned shell so that the central axis of the outlet pipecoincides with the central axis of the shell, a discharge pipe connectedto an opening provided at the bottom of the aforementioned tapersection, and an inlet pipe connected tangentially to the inner surfaceof the aforementioned cylindrical section for introducing a gas liquidtwo phase flow into the aforementioned shell, characterized in that theaforementioned inlet pipe is a spiral shape centered around the centralaxis of the aforementioned shell.

[0024] Furthermore, in each of the above configurations, theaforementioned shell has a taper section which narrows in a upwarddirection and which is formed on the top of the aforementioned cylindersection as an integral part of the cylindrical section.

[0025] Furthermore, in each of the above configurations, a plurality ofinlet pipes are provided, and these inlet pipes are connected to theaforementioned cylindrical section at the same vertical height positionwith an equal spacing between the pipes.

[0026] In addition, an outdoor apparatus according to the presentinvention is characterized by comprising a compressor, any one of theoil separators described above with an inlet pipe connected to thecompressor, a capillary tube connected to a discharge pipe of theaforementioned oil separator, a valve connected to the discharge pipe ina parallel arrangement with the capillary tube, an oil return circuitconnected to the capillary tube and the valve, an accumulator connectedto the oil return circuit and the compressor, a four way valve connectedto an outlet pipe of the aforementioned oil separator, and a heatexchanger connected to the four way valve.

[0027] Furthermore, an outdoor apparatus according to the presentinvention is characterized by comprising a plurality of compressors, theaforementioned oil separator with each inlet pipe connected to one ofthe plurality of compressors, a capillary tube connected to thedischarge pipe of the aforementioned oil separator, a valve connected tothe discharge pipe in a parallel arrangement with the capillary tube, anoil return circuit connected to the capillary tube and the valve, anaccumulator connected to the oil return circuit and the aforementionedplurality of compressors, a four way valve connected to an outlet pipeof the aforementioned oil separator, and a heat exchanger connected tothe four way valve.

[0028] In addition, in each of the outdoor apparatuses described above,the aforementioned valve is opened only during startup of thecompressor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a refrigerant circuit diagram of a refrigerating cycleaccording to an Embodiment 1 of the present invention.

[0030]FIG. 2 is a top cross-sectional view of an oil separator accordingto the Embodiment 1 of the present invention.

[0031]FIG. 3 is a side cross-sectional view of an oil separatoraccording to the Embodiment 1 of the present invention.

[0032]FIG. 4 is a diagram showing the relationship between L2 and theoil separation efficiency.

[0033]FIG. 5 is a diagram showing the state of a gas liquid two phaseflow in an oil separator.

[0034]FIG. 6 is a diagram showing the state of a gas liquid two phaseflow in an oil separator.

[0035]FIG. 7 is a diagram showing the relationship between L1 and theoil separation efficiency.

[0036]FIG. 8 is a diagram showing the relationship between L3 and theoil separation efficiency.

[0037]FIG. 9 is a top cross-sectional view of an oil separator.

[0038]FIG. 10 is a top cross-sectional view of an oil separator.

[0039]FIG. 11 is a refrigerant circuit diagram of a refrigerating cycleaccording to an Embodiment 2 of the present invention.

[0040]FIG. 12 is a top cross-sectional view of an oil separatoraccording to the Embodiment 2 of the present invention.

[0041]FIG. 13 is a side cross-sectional view of the oil separatoraccording to the Embodiment 2 of the present invention.

[0042]FIG. 14 is an internal structural diagram of a conventional oilseparator.

[0043]FIG. 15 is a partial longitudinal sectional view of a conventionaloil separator.

[0044]FIG. 16 is a structural diagram of a conventional oil separator.

[0045]FIG. 17 is a top cross-sectional view of a conventional gas-liquidseparator.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

[0046]FIG. 1 is a refrigerant circuit diagram of a refrigerating cyclewith an oil separator according to an Embodiment 1 of the presentinvention.

[0047] In FIG. 1, the refrigerating cycle comprises primarily a singleoutdoor apparatus 1, indoor apparatuses 20 a, 20 b, and a liquid pipe 30and a gas pipe 31 connecting the outdoor apparatus 1 and the indoorapparatuses 20 a, 20 b.

[0048] Furthermore, the outdoor apparatus 1 comprises primarily acompressor 2, an oil separator 3 connected to the compressor 2, a fourway valve 4 connected to the oil separator 3, a heat source side heatexchanger 5 with one port connected to the four way valve 4 and theother port connected to the liquid pipe 30, an accumulator 6 connectedto the compressor 2, an electromagnetic valve 7 connected to the oilseparator 3, a capillary tube 8 connected to the oil separator 3 in aparallel arrangement with the electromagnetic valve 7, and an oil returncircuit 9 connected to the electromagnetic valve 7, the capillary tube 8and the accumulator. The four way valve 4 is also connected to the gaspipe 31.

[0049] The indoor apparatus 20 a comprises primarily a throttle device21 a connected to the liquid pipe 31, and a load side heat exchanger 22a with one port connected to the throttle device 21 a and the other portconnected to the gas pipe 30. In a similar manner, the indoor apparatus20 b comprises primarily a throttle device 21 b and a load side heatexchanger 22 b.

[0050] Next is a description of the operation of the refrigerating cycleof FIG. 1.

[0051] When the refrigerating cycle is started, there will be caseswhere liquid refrigerant is sitting in the compressor 2. In such a case,when the compressor 2 is activated, a phenomenon known as foaming occurswhere the refrigerant liquid including the refrigerating machine oilinside the compressor 2 rapidly vaporizes and foams as a result of thepressure drop inside the compressor shell, so that large amounts of amixed liquid incorporating both the refrigerant and the refrigeratingmachine oil flow from the compressor 2 into the oil separator 3. At thistime, the electromagnetic valve 7 is opened and the mixed liquid ofrefrigerant liquid and oil is returned from the oil separator 3 to theinlet of the accumulator 7 via the oil return circuit 9. In this manner,even in the case where the inflow of oil into the oil separator 3increases temporarily, any possibility of the oil separator 3overflowing and oil being carried outside the outdoor apparatus systemis prevented.

[0052] Furthermore, when the refrigerating cycle enters steady-stateoperation, the electromagnetic valve 7 is closed. Oil carried out of thecompressor 2 along with the refrigerant gas is separated out by the oilseparator 3, reduced to a low pressure by the capillary tube 8, and issubsequently returned to the compressor 2 via the oil return circuit 9and the accumulator 6.

[0053] Next is a description of the structural details of the oilseparator 3.

[0054]FIG. 2 is a top cross-sectional view of the oil separator 3, andFIG. 3 is a side cross-sectional view of the oil separator 3.

[0055] In FIG. 2 and FIG. 3, 50 represents a shell of a cylindricalshape with both ends narrowed in tapered shape, and comprises acylindrical section, a lower taper section beneath the cylindricalsection, and an upper taper section above the cylindrical section. 51represents a cylindrical outlet pipe, which is inserted into the insideof the shell 50 through the apex of the upper taper section of the shell50, and this outlet pipe 51 is fixed so that the central axes of theoutlet pipe 51 and the shell 50 coincide. 52 represents a dischargepipe, which is fixed to a lower opening 50 a formed at the apex of thelower taper section of the shell 50. 53 represents an inlet pipe, whichis a cylindrical shaped pipe with a diameter D which is connected in atangential direction to the inner surface of the cylindrical section(the section which has not been narrowed in tapered shape) of the shell50. The tip 51 a of the portion of the outlet pipe 51 inserted insidethe shell 50 is positioned a distance L1 below the center of the tip ofthe inlet pipe 53 inside the shell 50, and a distance L2 above the loweropening 50 a of the shell 50.

[0056] Next is a description of the phenomena which occur in an oilseparator of this type of construction.

[0057] A gas liquid two phase flow consisting of refrigerant gas andrefrigerating machine oil discharged from the compressor 2 flows intothe shell 50 from the inlet pipe 53. The gas liquid two phase flow whichenters the shell 50 circles around and spirally sinks inside the shell50. As a result of this circling motion, a cyclone effect is generatedwherein the oil mist (fine particles of the refrigerating machine oil)is subjected to centrifugal forces and collides with, and adheres to,the inner surface of the shell 50, so that the oil mist suspended in therefrigerant gas is gradually separated out. Following separation of theoil mist, the refrigerant gas flows out of the outlet pipe 51, and therefrigerating machine oil adhering to the inner surface of the shell 50flows down the inner surface of the shell 50 under the effects ofgravity, is discharged from the discharge pipe 52, flows through the oilreturn circuit 9 via the capillary tube 8, and is then returned to thecompressor 2 via the accumulator 6.

[0058] Experiments revealed quite clearly that the oil separationefficiency of the refrigerating machine oil using this type of oilseparator varied depending on the position of the outlet pipe 51 insidethe shell 50, namely the relationship among the distance L1 between thetip 51 a of the outlet pipe 51 and the center of the tip of the inletpipe 53 inside the shell 50, the distance L2 between the tip 51 a of theoutlet pipe 51 and the lower opening 50 a of the shell 50, and thediameter D of the inlet pipe 53.

[0059]FIG. 4 is a diagram showing the relationship between L2 and theoil separation efficiency based on experimental results.

[0060] These experiments were conducted, assuming a large oil flow ratethrough the oil separator, under conditions including a refrigerant flowrate of 650 to 680 kg/h, an oil circulation ratio of 2.4 to 2.6%, and aninlet pipe diameter (inside diameter) D of 19.8 mm. The oil flow rate isthe product of the refrigerant flow rate and the oil circulation ratio.

[0061] In FIG. 4, a tendency can be seen for the oil separationefficiency to increase in accordance with increasing values of L2,although the degree of this increase in the separation efficiencyreduces at L2 values of approximately 5D, and at values greater than 5Dthe oil separation efficiency substantially levels off.

[0062] The reason why the oil separation efficiency is poor with theshort distance L2 is described below.

[0063] Namely, if the oil flow rate is large, and the distance betweenthe tip 51 a of the portion of the outlet pipe 51 inside the shell 50and the bottom of the shell 50 is small, then the gas currents revolvingin a spiral motion cause a rotating liquid film in the shape of a mortarto accumulate on the inner surface of the shell 50, as shown in FIG. 5,so that when separated oil is discharged from the discharge pipe 52, gasis also dragged in from the center, and a gas-liquid two phase flowflows out of the discharge pipe 52. Consequently, the oil flowing intothe oil return circuit 9 incorporates gas, so that the pressure loss inthe oil return circuit 9 increases and the return oil quantity cannot beensured sufficiently. As a result, the thickness of the oil filmadhering to the inner surface of the shell 50 increases further, and atthe bottom of the shell 50, liquid droplets will break away from thethick oil film again, resulting in a reduction in the oil separationefficiency.

[0064] At this point, the oil flow rate can be increased by reducing theflow passage resistance in the capillary tube 8 in the oil returncircuit. In such a case, however, if the inflow of oil into the oilseparator 3 reduces, the bypass volume of hot gas of the refrigerantwill increase, and the performance of the refrigerating cycle willdecline, so that using this method as means for increasing the oilseparation efficiency is problematic.

[0065] In contrast, if the distance L2 between the tip 51 a of theoutlet pipe 51 inside the shell 50 and the lower opening 50 a of theshell 50 is at least 5D, then the liquid film at the bottom of the shell50 is unlikely to be affected by the rotation of gas currents in aspiral motion within the shell 50, and as shown in FIG. 6, when theseparated oil is discharged from the discharge pipe 52, gas from thecentral region is not dragged down with the oil, so that the oil isdischarged as a single phase from the discharge pipe 52. As a result,pressure loss in the oil return circuit 9 can be suppressed, and theseparated oil can be discharged smoothly.

[0066] In this manner, by ensuring that the distance between the tip 51a of the outlet pipe 51 inside the shell 50 and the lower opening 50 aof the shell 50 is at least 5D, pressure loss within the oil returncircuit 9 can be suppressed, and a smooth discharge of the separated oilbecomes possible. Accordingly, by reducing the amount of accumulated oilinside the shell 50, and preventing any possibility of liquid dropletsscattered again in the lower sections of the shell 50, the oilseparation efficiency can be improved.

[0067]FIG. 7 is a diagram showing the relationship between L1 and theoil separation efficiency based on experimental results.

[0068] These experiments were conducted under conditions including arefrigerant flow rate of 400 kg/h, an oil circulation ratio of 0.5%, andan inlet pipe diameter (inside diameter) D of 19.8 mm.

[0069] In FIG. 7, a tendency can be seen for the oil separationefficiency to increase in accordance with increasing values of L1,although the degree of this increase in the separation efficiencyreduces at L1 values of approximately 5D, and at values greater than 5Dthe oil separation efficiency substantially levels off.

[0070] The reason why the oil separation efficiency is poor with theshort distance L1 is described below.

[0071] Generally, in a cyclone type oil separator, if the velocity ofthe gas flowing into the oil separator is reduced, the velocity of thecircling motion within the shell 50 reduces consequently, and liquiddroplets will hardly collide with the inner surface of the shell 50 dueto centrifugal forces, so that the liquid droplets remain swept up inthe circling gas and are discharged together with the gas, resulting ina reduction in the oil separation efficiency. In the case of the oilseparator incorporated in a refrigerating cycle, because the flow ratevaries depending both on variations in the operational state of therefrigerating cycle in accordance with variations in the loadingconditions and on control of the capacity of the variable flow typecompressor, the oil separation efficiency falls in the case where therefrigerant flow rate is small. The oil separation efficiency isdependent on the number of circulation made by the gas flow circlingaround inside the shell 50. Therefore, in order to increase the numberof such circulation, the distance between the tip of the inlet pipe 53inside the shell and the tip of the outlet pipe 51 should be maintained.This factor is reflected in FIG. 7, wherein by separating the positionsof the lower tip of the outlet pipe 51 and the tip of the inlet pipe 53inside the shell by a distance of at least 5D, the oil separationefficiency improves.

[0072] Accordingly, by separating the positions of the tips of theoutlet pipe 51 and the inlet pipe 53 inside the shell by a distance ofat least 5D, the number of circulation of the gas flow inside the shell50 necessary for oil separation can be ensured, even in the case wherethe refrigerant flow rate falls, so that the oil separation efficiencyimproves.

[0073] In addition, it is known that the gas liquid two phase flow ofthe refrigerant gas and the refrigerating machine oil inside the inletpipe 53 is affected by bends in the piping, which can cause variationsin the oil separation efficiency.

[0074]FIG. 8 is a diagram showing the relationship between the length L3of the straight pipe section from the tip of the inlet pipe 53 insidethe shell 50 and the oil separation efficiency, based on experimentalresults.

[0075] These experiments were conducted under conditions including arefrigerant flow rate of 400 kg/h, an oil circulation ratio of 0.5%, andan inlet pipe diameter (inside diameter) D of 19.8 mm.

[0076] In FIG. 8, a tendency can be seen for the oil separationefficiency to increase in accordance with increasing values of thelength L3 of the straight pipe section, although the degree of thisincrease in the separation efficiency reduces at L3 values ofapproximately 8D, and at values greater than 8D the oil separationefficiency substantially levels off.

[0077] The reason why the oil separation efficiency is poor with theshort distance L3 is described below.

[0078] Namely, if the length L3 of the straight pipe section is short,then a bias develops in the liquid distribution across a passagecross-section of the inlet pipe 53. Accordingly, if the straight pipesection is longer, this bias in the liquid distribution diminishes, andat lengths greater than 8D the flow form of the gas liquid two phaseflow stabilizes, and the oil separation efficiency improves.

[0079] If the straight pipe section of the inlet pipe 53 cannot be setto a value of at least 8 times the diameter of the inlet pipe 53 becauseof space restriction, a construction as shown in FIG. 9 can be used,wherein the inlet pipe 53 is bent at approximately 90° in the horizontalplane so as to roughly match the circumferential direction of the shell50, forming a first straight pipe section 54 a and a second straightpipe section 54 b.

[0080] In such a construction, with a gas liquid two phase flow ofrefrigerating machine oil and refrigerant gas flowing through the inletpipe 53, the refrigerating machine oil inclines to flow around the outerperiphery of the bent section between the second straight pipe section54 b and the first straight pipe section 54 a, and the refrigeratingmachine oil flows smoothly along the inner surface of the shell 50 whenentering the shell 50, so that the separation from the refrigerant gasis smoothly carried out to improve the oil separation efficiency.

[0081] Furthermore, as shown in FIG. 10, the inlet pipe 53 may be aspiral which is formed around the periphery of the shell 50 coaxiallywith the shell 50.

[0082] In such a construction, the refrigerating machine oil alsoinclines to flow around the outer periphery of the inlet pipe 53, sothat the oil separation efficiency improves.

[0083] In this embodiment, by forming not only the lower section, butalso the upper section of the oil separator 3 into a taper shape, thenumber of components can be reduced, and the thickness required toachieve the necessary strength can also be reduced, in comparison with acase that the top is formed as a flat lid, so that the apparatus can belightened.

Embodiment 2

[0084]FIG. 11 is a refrigerant circuit diagram showing a refrigeratingcycle according to an Embodiment 2 of the present invention, andrepresents the refrigerant cycle of FIG. 1 wherein two compressors areprovided in the outdoor apparatus, and these two compressors areconnected to an oil separator. In FIG. 11, those components which arethe same as, or correspond with components in FIG. 1 are labeled withthe same symbols, and their description here is omitted.

[0085] In FIG. 11, 2a and 2 b represent compressors, and each of thesecompressors is connected to the oil separator 3, via a check valve 10 aand a check valve 10 b respectively.

[0086] Next is a description of the operation of the refrigerating cycleof FIG. 11.

[0087] As there will be a case where liquid refrigerant is sitting inthe compressor 2 a and the compressor 2 b at the start of therefrigerating cycle, the electromagnetic valve 7 is opened to return themixed liquid of refrigerant liquid and oil from the oil separator 3 tothe inlet of the accumulator 6. As a result, any possibility of the oilseparator 3 overflowing and oil being carried outside the outdoorapparatus system is prevented. Furthermore, by starting the compressor 2a and the compressor 2 b one by one with a time lag therebetween, theeffect of preventing the overflow of the oil separator 3 is enhanced.

[0088] Furthermore, when the refrigerating cycle enters steady-stateoperation, the electromagnetic valve 7 is closed. Oil carried out of thecompressor 2 a and/or the compressor 2 b along with the refrigerant gasis separated out in the oil separator 3, reduced to a low pressure bythe capillary tube 8, sent into the oil return circuit 9, andsubsequently returned to the compressor 2 a and/or the compressor 2 bvia the accumulator 6.

[0089] Capacity control of the compressor 2 a and the compressor 2 b isconducted in accordance with the load, by suitable starting and stoppingof the compressors or by suitable adjustment of the operating frequencyof the compressors.

[0090] Next is a description of the structural details of the oilseparator 3.

[0091]FIG. 12 is a top cross-sectional view of the oil separator 3, andFIG. 13 is a side cross-sectional view of the oil separator 3.

[0092] In FIG. 12 and FIG. 13, 50 represents a shell of a cylindricalshape with both ends narrowed to taper sections. 51 represents acylindrical outlet pipe, which passes through the apex of the uppertaper section of the shell 50 and into the inside of the shell 50, andthis outlet pipe 51 is fixed so that the central axes of the outlet pipe51 and the shell 50 coincide. 52 represents a discharge pipe, which isfixed to a lower opening 50 a formed at the apex of the lower tapersection of the shell 50. 53 a and 53 b represent inlet pipes, which arecylindrical shaped pipes with a diameter D, positioned at the samevertical height on opposing sides relative to the central axis of theshell 50, and connected in a tangential direction to the inner surfaceof the shell 50. The tip 51 a of the portion of the outlet pipe 51inserted inside the shell 50 is positioned a distance L1 below thecenter of the tips of the inlet pipes 53 a, 53 b inside the shell 50,and a distance L2 above the lower opening 50 a of the shell 50.

[0093] Next is a description of the phenomena which occur in an oilseparator of this type of construction.

[0094] A gas liquid two phase flow of refrigerant gas and refrigeratingmachine oil discharged from the compressor 2 a and/or the compressor 2 bflows into the shell 50 from the inlet pipe 53 a and/or the inlet pipe53 b. While the gas-liquid two phase flow which enters the shell 50circles around and spirally sinks inside the shell 50, the oil mist issubjected to centrifugal forces and collides with, and adheres to, theinner surface of the shell 50, so that the oil mist suspended within therefrigerant gas is gradually separated from the refrigerant gas by theso-called cyclone effect. Following separation of the refrigeratingmachine oil, the refrigerant gas flows out of the outlet pipe 51, andthe refrigerating machine oil adhering to the inner surface of the shell50 flows down the inner surface of the shell 50 under the effects ofgravity and is discharged from the discharge pipe 52.

[0095] The pressure loss of the oil separator 3 is dependent on thediameter of the inlet pipes. Therefore, if only one inlet pipe is usedand the diameter of that pipe is excessively increased in order toreduce the pressure loss at the time when refrigerant is flowing fromtwo operating compressors, the oil separation efficiency declines due toa reduction in the centrifugal separation effect at the time when onlyone compressor is operated and the flow rate drops. Consequently, byproviding one inlet pipe for each compressor, pressure loss can bereduced, and any reduction in oil separation efficiency can be preventedat the time when only one compressor is operational. Furthermore, in asystem with two compressors, the reliability of the refrigerating cyclecan be improved at low cost by separating the oil carried out of thecompressors with a single oil separator, and preventing depletion of thelubricant in the compressors.

[0096] Furthermore, by positioning the inlet pipe 53 a and the inletpipe 53 b at the same vertical position within the shell 50 with anequal spacing between the pipes around the inner surface, the trajectoryof the refrigerant gas entering from one inlet pipe will not interferewith that from the other inlet pipe, so that gas flow turbulence withinthe shell 50 can be suppressed, and any reduction in oil separationefficiency during operation of the two compressors can be prevented.

[0097] In this embodiment, a description was provided for the case oftwo inlet pipes, but even in the case of three or more inlet pipes, thesame effects can be achieved by positioning the inlet pipes at the samevertical position (the same height) within the shell, with an equalspacing between the pipes around the inner surface. Furthermore, thediameter of each of these plurality of inlet pipes can be altered inaccordance with the flow rate of the refrigerant or the capacity of thecompressors.

[0098] In an oil separator according to the present invention, thedistance between the shell opening and the tip of the outlet pipe insidethe shell is at least 5 times the inside diameter of the inlet pipe.Therefore, even if the quantity of oil flowing into the oil separatorincreases, a reduction in the oil separation efficiency can beprevented.

[0099] Furthermore, in an oil separator according to the presentinvention, the tip of the outlet pipe inside the shell is positionedbelow the center of the inside diameter of the inlet pipe at a distanceat least 5 times the inside diameter of the inlet pipe, so that the oilseparation efficiency can be maintained at a high level across a widerange of refrigerant circulation flow volumes.

[0100] Furthermore, in an oil separator according to the presentinvention, the inlet pipe has a straight pipe section connected to thecylindrical section of the shell, and the length of this straight pipesection is at least 8 times the inside diameter of the inlet pipe, sothat the oil separation efficiency can be increased at low cost even inthe case where the gas flow rate is low.

[0101] Furthermore, in an oil separator according to the presentinvention, the inlet pipe is a bent pipe with a first straight pipesection connected to the cylindrical section and a second straight pipesection positioned at a 90 degree angle to the first straight pipesection in the direction of the aforementioned shell, or alternatively,in an oil separator according to the present invention, the inlet pipeis a spiral formed around the central axis of the shell, so that theseparation efficiency can be improved even in the case where theinstallation space is limited.

[0102] In addition, the shell comprises a taper section narrowing in aupward direction, which is formed on the top of the aforementionedcylindrical section as an integral part of the cylindrical section. So,in comparison with a case where the top is formed as a flat lid, thenumber of components can be reduced, and the thickness required toachieve the necessary strength can also be reduced, so that theapparatus can be lightened.

[0103] In addition, a plurality of inlet pipes are provided, and theseinlet pipes are connected to the cylindrical section at the samevertical position with an equal spacing between pipes. Consequently,pressure loss can be reduced, and any reduction in oil separationefficiency can be prevented when only one compressor is operated.Furthermore, in a system with two compressors, the reliability of therefrigerating cycle can be improved at low cost by separating the oilcarried out of the compressors with a single oil separator, andpreventing depletion of the lubricant in the compressors. Moreover, thetrajectory of the refrigerant gas entering from one inlet pipe will notinterfere with that from the other inlet pipe, so that gas flowturbulence within the shell can. be suppressed, and any reduction in oilseparation efficiency during operation of the two compressors can beprevented.

[0104] In addition, an outdoor apparatus according to the presentinvention comprises a compressor, an oil separator as described abovewith an inlet pipe connected to the compressor, a capillary tubeconnected to the discharge pipe of this oil separator, a valve connectedto the discharge pipe in a parallel arrangement with the capillary tube,an oil return circuit connected to the capillary tube and the valve, anaccumulator connected to the oil return circuit and the compressor, afour way valve connected to the outlet pipe of the oil separator, and aheat exchanger connected to the four way valve, so that the operatingefficiency of the apparatus improves.

[0105] Furthermore, an outdoor apparatus according to the presentinvention comprises a plurality of compressors, the aforementioned oilseparator with each inlet pipe connected to one of the plurality ofcompressors, a capillary tube connected to the discharge pipe of the oilseparator, a valve connected to the discharge pipe in a parallelarrangement with the capillary tube, an oil return circuit connected tothe capillary tube and the valve, an accumulator connected to the oilreturn circuit and the plurality of compressors, a four way valveconnected to the outlet pipe of the aforementioned oil separator, and aheat exchanger connected to the four way valve, so that the operatingefficiency of the apparatus improves.

[0106] In addition, the valve is opened only during startup of acompressor, so that any overflow of the oil separator can be prevented,even during startup of a compressor when the oil flow rate into the oilseparator increases temporarily.

1. An oil separator comprising a shell having a cylindrical section anda taper section which narrows in a downward direction and which isformed as an integral part at a bottom of said cylindrical section, anoutlet pipe which is inserted through a top of said shell so that acentral axis of said outlet pipe coincides with a central axis of saidshell, a discharge pipe connected to an opening provided at a bottom ofsaid taper section, and an inlet pipe connected tangentially to an innersurface of said cylindrical section for introducing a gas liquid twophase flow into said shell, characterized in that a distance betweensaid opening and a tip of said outlet pipe inside said shell is at least5 times an inside diameter of said inlet pipe.
 2. An oil separatorcomprising a shell having a cylindrical section and a taper sectionwhich narrows in a downward direction and which is formed as an integralpart at a bottom of said cylindrical section, an outlet pipe which isinserted through a top of said shell so that a central axis of saidoutlet pipe coincides with a central axis of said shell, a dischargepipe connected to an opening provided at a bottom of said taper section,and an inlet pipe connected tangentially to an inner surface of saidcylindrical section for introducing a gas liquid two phase flow intosaid shell, characterized in that a tip of said outlet pipe inside saidshell is positioned below a center of an inside diameter of said inletpipe at a distance at least 5 times said inside diameter of said inletpipe.
 3. An oil separator comprising a shell having a cylindricalsection and a taper section which narrows in a downward direction andwhich is formed as an integral part at a bottom of said cylindricalsection, an outlet pipe which is inserted through a top of said shell sothat a central axis of said outlet pipe coincides with a central axis ofsaid shell, a discharge pipe connected to an opening provided at abottom of said taper section, and an inlet pipe connected tangentiallyto an inner surface of said cylindrical section for introducing a gasliquid two phase flow into said shell, characterized in that said inletpipe has a straight pipe section connected to said cylindrical section,and a length of said straight pipe section is at least 8 times an insidediameter of said inlet pipe.
 4. An oil separator comprising a shellhaving a cylindrical section and a taper section which narrows in adownward direction and which is formed as an integral part at a bottomof said cylindrical section, an outlet pipe which is inserted through atop of said shell so that a central axis of said outlet pipe coincideswith a central axis of said shell, a discharge pipe connected to anopening provided at a bottom of said taper section, and an inlet pipeconnected tangentially to an inner surface of said cylindrical sectionfor introducing a gas liquid two phase flow into said shell,characterized in that said inlet pipe is a bent pipe having a firststraight pipe section connected to said cylindrical section and a secondstraight pipe section bent at a 90 degree angle to said first straightpipe section in a direction of said shell.
 5. An oil separatorcomprising a shell having a cylindrical section and a taper sectionwhich narrows in a downward direction and which is formed as an integralpart at a bottom of said cylindrical section, an outlet pipe which isinserted through a top of said shell so that a central axis of saidoutlet pipe coincides with a central axis of said shell, a dischargepipe connected to an opening provided at a bottom of said taper section,and an inlet pipe connected tangentially to an inner surface of saidcylindrical section for introducing a gas liquid two phase flow intosaid shell, characterized in that said inlet pipe is a spiral shapecentered around a central axis of said shell.
 6. The oil separatoraccording to any one of claim 1 through claim 5, wherein said shellcomprises a taper section which narrows in an upward direction and whichis formed on top of said cylinder section as an integral part of saidcylindrical section.
 7. The oil separator according to any one of claim1 through claim 6, wherein, a plurality of said inlet pipes areprovided, and said inlet pipes are connected to said cylindrical sectionat an identical vertical height position and with an equal spacingbetween said inlet pipes.
 8. An outdoor apparatus characterized bycomprising a compressor, the oil separator according to any one of claim1 through claim 6 with an inlet pipe connected to said compressor, acapillary tube connected to a discharge pipe of said oil separator, avalve connected to said discharge pipe in a parallel arrangement withsaid capillary tube, an oil return circuit connected to said capillarytube and said valve, an accumulator connected to said oil return circuitand said compressor, a four way valve connected to an outlet pipe ofsaid oil separator, and a heat exchanger connected to said four wayvalve.
 9. An outdoor apparatus characterized by comprising a pluralityof compressors, the oil separator according to claim 7 with each inletpipe connected to one of said plurality of compressors, a capillary tubeconnected to the discharge pipe of said oil separator, a valve connectedto said discharge pipe in a parallel arrangement with said capillarytube, an oil return circuit connected to said capillary tube and saidvalve, an accumulator connected to said oil return circuit and saidplurality of compressors, a four way valve connected to an outlet pipeof said oil separator, and a heat exchanger connected to said four wayvalve.
 10. An outdoor apparatus according to any one of claim 8 andclaim 9, characterized in that said valve is opened only during startupof said compressor.